Electron emission material



1932- M. N. FREDENBURGH 87 51 nmacmon EMISSION MATERIAL Filed July 11, 1928 PREPARATION OF .BARIUM STRONTIUM CALCIUM CARBONATE BAR/um NITRRTE C]? 66.2. (51%. AMMmv/u/w CARE ONAT'E STRO/VT/UM N/TIFHTE C]? 4.3.0 6M3. C7 LUMP //00 GM 5. CALCIUM lV/TRATE GPA-2a Cims.

AMMoMu/v: HYDPGX/DE .DJSSOLVED IN DIST/LLED WATER 6.7 ($45.30) 470 6M5.

960 ML. AT 90'- [00C.

F/LTERED Tw/cE.

FILTERED Tw/cE.

SOLUTION No. I. SoLuT/oN No. 2,.

OO/WL. SOLUTION No. .2.

SOLUTION No.2 ADDED To SOLUTION No. AT'Co/vsTANT PAT: VV/TH sT'lRRlNCy So THAT TIME OF PRECIPITATION ls 5/Vl/N.

BAR/UM srno/vr/um CALCIUM Cameo/mm PLus WATER, PLUS Hm/wa/v/u/w lV/TRATE.

TRANsFERREpI 7'0 BucHMER FILTER.

WAsHEb W/rH .DISTILLED WATER fso-/aac.) UNTIL FREE FRO/v1 NITRATES.

VACUUM F/LTERED.

PPT. DRIED A7- /oo- /2oc.

BoTTLEp.

INVENTOR MN. FR EDENBURQH ATTORNEY Patented Au 9.1932

max N. rnn'nnnnunen, or East onmen, new

HOUSE LAMP COMPANY, A. CORPORATION OF PENNSYLVANIA nLns'raon niurssrorf i Application filed July- 11, 1928. sum in. 292,087.

This invention relates to electron-emitting:

electrodes and more particularly to electronemitting cathodes of the oxide coated type and comprisesessentially in a process (and the product) of producing substantially pure intimately admixed alkaline earth metal carbonates which may be employed in producing alkaline earth metal oxide coated cathodes for electron-emitting purposes. The products of this invention comprise admixed alkaline earth metal carbonates to which have been imparted a preferred and. definite crystalstructure'not heretofore obtainable andthe oxide coated cathode repared therefrom.

This invention is an improvement of the process of preparingelectron-emitting cathodes as set forth in the patent of Duncan MacRae,.'No. 1,812,103, entitled Electronemitting devices and method of making, which patent is assigned tothe Westinghouse Lamp Company, the assignee' of the present application;

' The process described in said patent contemplates applyinga coating of alkaline earth metal carbonates to the surface of a metallic cathode by forming an inorganic suspension of the carbonates in water or other suitable liquid which is inert with respect to.

the carbonates and which may be removed by heat without decomposition. Thereafter the composite cathode is suitably heated in an atmosphere of carbon dioxide to cause the coated material to adhere to the metal base and to remove'the 'susp ension medium. This coating process maybe repeated any number of'tinies so as to obtain heavier'deposits of the alkaline earth metal carbonates and may be made a continuous one if desired.

The resulting coating being comprised of unaffected by atmospheric gases and cathodes so coated may be kept indefinitely without deterioration before being incorporated in an electron discharge device. After being mounted in an electron discharge ,device, this carbonate coating may be rendered in an electronically active condition by highly heating the composite cathode during the exhaust procedure whereby the carbon oxide content of the 'coatingis substantially removed, leavalkaline earth metal carbonates is stable and ing a residue of anhydrous alkaline earth metal oxides which are adherent to the sin;

.\face of the metal base. In he practice of the in said patent ithas been found thatthe dispersion, purity, particle size, relative proportions 'of thecolnponent alkaline earth metal carbonates, etc., exert a considerable influence mam, Assrenon 'ro wasrnm rocess'as disclosed onthe application of the carbonate to the filament, as well as in effec the efiiciency and life'of the electron emissionof the hot composite cathode.

' In the process of coating as disclosed in said patent the preferred admixture of alkaline earth meta lcarbonates employed is com risedof barium and strontium carbonates, alt ough other admixtures of the alkaline earth metal carbonates are antici ated asfalling within the scope of the coating composition.

Thelcommon practice heretofore has been to employaiiy commercial grade of chemi- -cal1y pure alkaline earth metal carbonate as may be purchase'able upon the market, comminute the same, admix mechanically in the desired proportion and thereafter form an emulsion or suspension of the admixed materials in the desired medium for, coating. Separate aiid'independent lots of carbonate material as obtained on the market. were 1 found to vary widely in thedegree of purity; particle size, absorbtive properties towar the carrier fluid and density, etc., which caused variable results with respect to the life and efliciency of the resultant electron dis charge device within which the coated cathodes were employed. Moreover, at times dif-. ficulty was experienced in obtainin a uniform admixture of the carbonates wit out too finely comminuting the particles during the admixing process. Some difliculty was also experienced in maintaining durin the coating operation a uniform mix of t e component carbonates.

' One of the objects of this invention is to reduce the variable operating characteristics heretof gxide coated type. I

Another ob ect of this inventionis to provide a; high grade coating material for oxide coated cathodes which is comprised of umore encountered in hot cathodes of the formly admixed substantially pure carbonates I of the alkaline earth metals. tions and speed of mixing.

Another object of this invention is topro- .When barium carbonate alone is prepared vide a coating material for oxide coated filaby this general method the product proments comprised of intimately admixed alduced, regardless of the physical constants kaline earth metal carbonates which is uni of preclpitation when dried, is always more ture, pressure, concentration of the two soluform in composition, of a coarsely crystalor less flufly and'finely divided. When line structure and of a high degree of purity. strontium carbonate. alone is prepared by Another. object of this invention is to prothis general method, variation 1n precipita- 1o vide an'oxide coated cathode comprised of a tion conditions may produce a. material refractory metal filament base and a coating I either dense or light and fiuflt'y. When adof alkaline earth metal o'xidesin such a physmixtures of barium and strontium carical state of intimate admixture, purity, parbonates which heretofore have been emp 1oy-' ticle size, etc., that uniform operating results ed as a coatingmaterial in this process are 15 a bt i d th f formed by simultaneous precipitation, the

Anothe ct of this invention isto prodensity and phwre of the 5 vide a commercial process for preparing the cipitate may be us vary widely-by I substantially pure carbonates of the alkaline varying the precipitation conditions. T

earth metals in an intimately admixed state which process would be operable. to produce r effects primarily the absorbent or suspension this productconsistently.

properties of the material, thus altering the Other objects and advantageswill be .apcoating procedures considerably.

parentas .the process is more fully disclosed. I When calcium carbonate alone is prepared 5 In pre aring oxide coated cathodes of the by this general method the efi'ect of the phyinvention, the physical state of the admixed crystal structure of the resultant product is carbonates of the alkalineearth metals-has pronounced. By varying the precipitationa pronounced efi'ect upon the operating char conditions, two crystal forms or admixtures 3o acteristics of the composite. cathode. It is of these two forms of calcium carbonate may desirable from many standpoints to obtain a be obtained. a, highly-intimate dispersed admixture of the This variation in density'of the carbonates, I i

and in ,a coarse grained crystalline form due t0 variable precipitation conditions, 86

ao character fallm within the scope of this sical constants of precipitation pan the The more common and stable form is cal- V carbonate inaterialfi more intimate than is .cite which maybe precipitatednormally from obtainable bymechanical admixture. It is cold 'or medium ,warm solutions. Aragonite',

also desirable to retain a-relatively coarse but which is the second form of calcium caruniform particle size sof the admixed carbonate,may be precipitated. when the tem-' bonates, which' is practically impossible to perature of the calcium solution is held above obtain by 'mechanical admixture means. It 85 C. during precipitation.

j is necessary to retain a high degree of purity 40 in the components of the coating material. talstructure of the calcium carbonate may oughly understood as to which of the alkaline; taneously with either one or both of the other I earth metal oxides the phenomena of electron alkaline earth metal carbonates and that the emission. is due, recent researcheshaveindiprecipitation of thearagonite crystal form cated thati'n-a composite-oxidecoating such of calcium has a pronounced efi'ect uponthe as-may be formed by this process the emiscrystal structure of the simultaneously presion quality at 'the present operating tem-' cipitated admixed alkaline earth carbonates. per'ature's .is due to he barium component I have foundthat the addition of 'calclum thereof. It is commonly considered that the salts to admixed bariumand strontium solufunction of the remaining component or comtions and simultaneous precipitation of the ponents (SrO and -OaO) is in the nature of three alkaline earth metals under such con- I have determined that the aragonite crysw "Whereas heretofore it has not been thorbe obtained readily when precipitated simul-' an inert or'retaining structure serving either ditions thatthe ara'gonite type of crystal I as a carrier for the electron-emitting constitstructure is developed, completely alters the 9 uent, a, m t t o di e ing medium.- size of and the ysical state of the barium It is essential that the activating constituent and strontium carbonates and they partake of the filament BaO) be present in theof the sanfe type of crystal structure as the oxide coating in a finely dispersed condition calcium, and" form isomorphous crystals of for best electron emission results. strontianiteand witherite which also belong v The preparationof pure barium,strontium to the; rhombic system of crystallization.

' and calcium carbonates maybe accomplished Such a precipitation or formation of this s gby adding to an aqueous solution of thepure rhombic crystal structure is not normally ob- "nitrates, a solution \of alkali metal or .amtained by precipitating the barium and stron- I monium carbonates. The physical nature of tium aloneunderthesame conditions. This the precipitated material varies "with the efi'ect on the crystalstructure of theaggreconstantsof precipitation, such as temperagate precipitate .is increasingly pronounced with increased calcium content becoming apparent with as little as .5% CaCO and increasing until at approximately 10 to 20% calcium the desirable effect on the crystal structure which is desirable for the purpose of my invention is obtained. Larger percentages than 20 percent CaCO may be employed but are not essential to produce the effect which I have utilized in the practice of my invention serving only to increase the degree of coarsening of the individual crystals of the precipitated carbonates.

I have also determined that the rate of precipitation has a direct bearing upon. the

ultimate particle size and particle size contrast and for the purpose of my invention it appears desirable to effect the production of the admixed carbonates in such a manner as to cause the resulting crystals to be of nearly the same size and have at least a constant maximum particle size contrast. The per cent calcium present-in the solution (dilution) controls the maximum obtainable particle size whereas the rate of precipitation controls the particle size contrast.

It is common practice in many arts in order to obtain intimate mixtures of two or more components to simultaneously precipitate the components from aqueous solutions. Intimate admixtures of the alkaline earth carbonates may be prepared in this manner, but I have determined, however, that simultaneous precipitation of alkaline earth metal carbonates alone does not accomplish the desired effect as the crystal structure and particle size contrast of the material is an important factor in the'preparation of and subsequent activation of oxide coated cathodes by this method. Simultaneous precipitation of the carbonates must be accomplished under the certain conditions of temperature of solutions, dilution of solution, component admixtures, rate of precipitation, etc., so as to cause the formation of a definite physical state (particle size) and crystalline structure of the precipitate.

In order to ensure absolute purity in theresultant carbonate product, precipitation with alkali metal carbonates should be avoided. I prefer to employ ammonium carbonate and have found that the normal ammonium carbonate is a preferable compound to employ.

" ammonium compound are readily decomposed and volatle 1n vacuo.

- Another factor influencing my process from a commercial standpoint is the factor of dilution of solution, that is, the proportion of solids therein. Should the process of precipitation be conducted in too concentrat ed a solution, difiiculty in preventing occlusion of impurities in the crystal structure is encountered. This occlusion of impurities decreases with increased dilution until at approximately a concentration of 15.0 percent Greater or lesser dilutions may be employed however, without departing from the nature of myinvention. as regards the specific use of calcium as the extent of dilution has no apparent effect on the effect of the aragonite structure formation on the admixed barium and strontium precipitates.

Having broadly outlined the scope and nature of my invention I Will specificallydescribe my process as developed to form an admixture of alkaline earth metal carbonates which-may be utilized as the coating material on hot cathodes in electron discharge devices.

I first form a solution of the mixed nitrates of the alkaline earth metal containing approximately 15.0 percent total solids comprised as follows Barium nitrate (C. Pi'anhydrous) l 66.2 gins.

Strontium nitrate (C. P. anhydrous). l gms Calcium nitrate (C. P. 4 H 0) 4.4.2 gins. Distilled water 960 m. 1.

The nitrates are dissolved in the water contained in a Pyrex glass beaker of two liters capacity, by heating to 80 C. The solution is then filtered twice by gravity through a No. 14: l/Vhatman filter paper. This solution I'will refer to as solution #I.

As previously noted, other concentrations of solution may be employed if desired, but I have found that in general the difficulty'of washing free of impurities increases with increased concentration of total solids and that this concentration is most satisfactory from all standpoints.

I next prepare a solution of normal am monium carbonate (Spec. Grav. 1.130 at 25 C.) :This solution is prepared as follows Ammonium carbonate C. I. lump) 1100 gms. Ammonium hydroxide (C. P. S. G. Distilled water L 1987 m. 1.

beaker of 1 liters capacity, the ammonium carbonate is then added and the contents heated to and maintained at approximately 40 C., with occasional stirring until solution is complete. The solution is then filtered twice by gravity through a No. 14 Whatman filter paper. This solution I will refer to as solution #11.

In preparing theprecipitated. carbonates of the alkaline earth metals by my process I first heat solution #I in a'Pyrex glass beaker of two liters capacity to a temperature not less than 90 C. To this heated solution I add at a constant rate 200 m. l. of solution #II which has been preheated to. 30 (1., maintaining at all times a vigorous agitation of the solution during precipitation. With this particular proportionate mixture of alkaline earth metal carbonates I have found thatthe rate of addition of the normal aim-- monium carbonate solution to eifectpreclpi- 'tation of the carbonates should be such that total addition of the 200 m. L of solution II he efifected in approximately one minute.

.This rate of precipitation is the factor which difierences in the crystals of the precipitate appears to directly effect the. particle size and should be maintained a constant factor between successive precipitations.

With other dilutions of solution or relative proportion of barium to strontium to calcium therein this rate may be varied. The

temperature of the solution, however, must be maintained above 85 C. and.preferably between 90 and 100 C. at all times during precipitation in order to obtain the preferred I crystal structure of the precipitate.

After precipitation, the material is allowed to settle, the clear liquid decanted, and the material then washed into a Biichner funnel fitted with No. 50 Whatman filter paper- Thematerial should be thoroughly washed with hot water on the. filter until free from nitrates and the excess; moisture removed by application of vacuum to the filter. The particular coarsely crystalline structure which I obtain by myprocess facilitates washing free of impuritiesby permitting rapid passage of the washing fluid through the pores of the precipitate and filter.

The precipitate is then transferred to a Pyrex glass tray and dried at-approximately 110 C. When thoroughly dried and anhydrous, the composition of this material will be 50% barium carbonate, 30% strontium carbonate and 20% calcium carbonate. The material, although coarsely crystalline andrather dense, will readily pass a 325 mesh screen without any milling.

. This material is now ready for the coating process which is described in the previously mentioned patent of Duncan MacRae, No.

. 'necessity of-obtaining a coating material in 50 As before stated that in addition to the which the activating constituent thereof (barium) is finely disseminated throughout the mass, it is also necessary tomaintain a certain degree of coarseness or particle size within the coating material.

The exact reasons therefore are not at this time thoroughly understood but it is known b simultaneously precifitating the admixed a kaline earth metals in such a manner as to cause the formation of a coarsely crystalline product thereof and-by regulating the recipitating time interval to holdthe indivi ual particle sizes within a certain narrow par ticle size range, I am enabled to subsequently subdivide the said crystals 'toany preferred particle size by proper supervision overthe milling operation. In this manner I ,subdivide the crystalline precipitate to a degree which vives the best results when the material -is'appl1ed to and utilized one hot cathode in an electron discharge device.

I employ the following method in preparing a suspension of the carbonate material for coating a filament of the size which is employed in electron discharge devices of the power tube type, known to .the trade as the 171-A tube, in which the filament has thedimensional measurement of approximately .0047 X .00075 inches. 1

I prepare anadmixture of 95 grams of the dry anhydrous carbonates with 50 ml. distilled water. To this material I add a suitable binder material such as barium .nitrate or barium nitrite in amounts up to 5.0 per cent (by weight). I prefer to employ as a binder the barium nitrite (Ba (N0 as this compound melts and dissociates'in vacuo at a lower temperature than the nitrate compound giving thereby a bonding action at a lower temperature. I

- This mixture I place in a porcelain ball mill of approximately one quart capacity containing approximately 700 grams of flint pebbles of from A to inches in diameter. The mill is then revolved at a rate. of approximately '100 R. P. M. for a period of 1% to four hours. The ball milled carbonates are then placed in the coating cups and the filamentary cathodes coated by a continuous process substantially.

as described in the patent of Duncan MacRae, No. 1,812,103.

To obtain suitable deposits of the alkaline earthmetal carbonates upon the filamentary material above mentioned, it is not necessary to pass the filament through the process more than four times to obtain a deposit weighing approximately 1.0 m. .g. per 10 0. m. (i 10%). The speed through the coating cup'is' maintained at approximately 12 meters per minute and the temperature of the drying ovens through which CO is continually passed is maintained at from 700 to 900 C.

I am enabled to retain in the coating, the crystalline character of the carbonatematerial until it is subjected to complete decomposition during the evacuation procedure of the electron discharge device of whiclrit is an incorporated part.

Owing to the fact that the anhydrous oxides of the alkaline earth metals rapidly absorb moisture and CO from the air, it is difii cult to detect physical differences from oxide v 85 C. and simultaneously coated filamentary cathodes preparedfrom carbonates produced by'the practice -ofmy invention, and cathodes. repared from carybonatesproduced .by ot or processes after the same have been decomposed'invacuo to the alkaline earth 'metal oxides. I have found, that cathodes formed of carbonates prepared by my process exhibit. a greater uniformity in operating efliciency, life and maintenance over oxide coated cathodes heretofore prepareda- In addition thereto the electromc efiiciency, life and maintenance ofcathodes is more consistent and reliable from 'lot to. lot than heretofore obtainable.

- Whiledl do not wan't to be restricted to any theory I believe the unusual and excellent results Irobtain from the use ofthe. carbonate product of my invention is-due to the fact 0 that I obtain in the racticeof my invention, a coating material 1I1 Whl0h the activating constituent (barium) is finely andv uniformly dispersed throughout and in addition thereto the natureof the crystal structure ofthe precipitate and the permissible control orer the ultimate particle size thereof which'may comprise the actual coating on the cathode permits me to develop the maximum adhesive and electron emissive' properties of the coating material.

Whereas I have disclosed a specific; process for preparing an alkaline earth metal car bonate material for electron emission pur-/ poses and given the details of the process ofcoating the same upon a filamentary cathode,.

it is obvious that theremay be many variations made in the specific steps employed and a A the composition-of the'coating material employedtherein-without departing from the 40 nature of my invention and s'uch variations are anticipated as may fallvvith in the following claims. 3

-What is claimed is: '1. The method of forming intimate ad mixtures of alkalin arth metal carbonates which, comprises f rminga solution of barium, strontium and calcium salts in the desired proportion, heating the solution to temperatures approximating but in excess to V precipitating therefrom the alkaline eartli metals as a carbonate by the addition of avsplution ofnor- Inal ammoniumr carbonate.

2 The process of forming an intimate mixture of substantially pure barium and strontium carbonatescontaining not less than .5 per cent calciumcarbonates ina crystalline form isomorphous with the aragonite crystal structureof calcium carbonate which comprises admixing soluble salts of those metals in the desiredproportion-to form approximately 15.0 percent, solution, simultaneously precipitating the alkaline earth metal carbonates therefrom in a interval of- '@5 time through the addition thereto of a warm solution of normal ammonium carbonate, and maintaining during said precipitation procedure'a' solution temperature approximating but higher'than', C. v 1 *3. The process of formingintimate m'ixtures;of alkaline earth metal carbonates iso-,

morphous with respect to the aragonite'crystal structure of calcium carbonate which comprises forming a dilute water' solution of barium and strontium" nitrates in desired 5 relative proportions addingthereto -from .5% to 20% calcium nitrate, heatipg the solu: tion to .temperatures a proximating Sbut" :higher than 85Wneously precipi tating thealkalin metals as carbonates 8o therefrom by adding thereto at a constant rate. a warm solution of normal ammonium L'carbofiate. 4 .A". An electrode having a' coating, comprising a'mi'xtureof substantially-pure alkaline g5 earth-metal carbonates having a crystal strum ture isomorphous to'aragonite.

.5, A coated filament suitable for usein an je lectron discharge device formed; of about 50% of barium carbonate, 30% of strontium a. carbonate and about 20% of calcium carbonate, said carbonate material being-comprised of fractured crystals of substantially pure- 3- a'ragon'ite and isom orphous strontianite and witherite.

. I '95 6 An electrode haying a coatingcompris- I hr of the carbonatesof at leastone of the al aline earth metalsbarium or strontium associated with calcium carbonate in amounts structure of said material being substantial; 'ly isomorphous with calcium carbonate in, the aragonite crystal form. 7. As an article of manufacture, admixtures of alkaline earth metal carbonates con taining at least .5 percent calcium carbonate in which the 'calciumfcarbonate thereof is identifiable a's-b elonging to the-rhombicsystern of'crystal structure of the orthorhombic bipyramidal class, and the barium and strontium 'carbonates isomorphous' thereto.

81 As an article of manufacture, admix tures of alkaline earth metaLcarbonates-containing at least .5 percent calcium carbonate in, which the calcium carbonate thereof is identifiable as belonging -to the rhombic sys= tem of crystal structure of the orthorhom bio bipyramidal class, and the barium and strontium carbonates isomorphous thereto, said material containing up to .5 ipercent bariuni nitrite as a binder material;

QaA coating material for use in forming I cathodes of the oxide coated type comprised of approximately 50 per cent barium ,car-

bonate, approximately 30 per cent, strontium carbonate,'about 20% calciumcarbonat'e and containing approximately 5;% barium nitrite. f l

10. Themethod of forming i-ntimate admixturef of alkaline earth metal carbonates above approximately .5 percent the crystal 1 00 having a crystal structure isomorphous to calcium carbonate in the aragonite form,

' which comprises forming an aqueous solution of alkaline earth metal compounds admixed in the desired proportions, precipitating said solution with normal ammonium carbonate maintaining during said precipitation a so-' lution temperature of about 85 C.

1'1 .The method, of forming intimate admixtures of alkaline earth metal carbonates having a crystal,structure'isomorphous to. calcium carbonate in the aragonite form and h'avingia predetermined particle sizecontrast which comprises forming an aqueous solution of alkaline earth metal compounds ad-- mixed in the desired proportions, precipi-l tating said solution with normal ammon um carbonate, maintaining during said precipitation a-solution temperature of about 85 G.- and limiting the time interval of comple tion of said precipitation.

. 12. The method of forming coarsely crystalline intimate admixtures of alkaline earth metal carbonates which are suitable for use in the forming of electron emitting oxide coated type cathodes, which comprises forming an aqueous solution of barium and stron-,

tium salts in the desired proportions, adding theretofrom .5 to 20.0 per cent calcium salts,

precipitating said solution with normal am monium carbonate, maintaining during said precipitating reaction a solution temperature not less than about 85 G:

/ l3. The method of forming coarsely crysotallineintimate admixtures of alkaline earth metal carbonates suitable for use in the form-' ing of electron emitting oxide coated type cathodes which comprises forming a dilute aqueous. solution containing barium andstrontium salts inthe desired proportion,-

' adding thereto from .5 to 20 per cent water soluble calcium salts, precipitating said solution with normal ammonium carbonate,

maintaining a solution temperature during said precipitation of not less than 85 0., and limiting the time interval of the completion of theprecipitati greaction. v v

forming substantially 14. The method .0 pure coarsely crystalline'intimate admixed alkaline earth metal carbonate admixtures which comprises preparin gonite.

A. coating composition from .WhlClI about a 15 per strontium, and calcium saltsadmixed in the desired proportion with a'solution of normal ammonium carbonate, while maintaining solutlO! temperatures above approximately 85 r .16. The method of preparing coarsely crystalline intimate admixtures of alkaline earth metal carbonate compounds which comprises effecting the separation of said carbonate compounds at temperatures above about 85 C. from an aqueous solution containing their salts admixed in the desired proporduced(compr1sing a suspension of substantially pure alkaline. earth metal carbonate compounds the crystal structure of said carbonates being isomorphous to that of ara- 19. electronically active cathodes may be produced comprising a suspension of barium and strontium carbonate in approximately equal proportions and from .5,to 20 per cent'calcium carbonate, the crystalstruct'ure'of said calcium carbonatewbeing that of aragonite and the'crystal structureof the bariumand strontium carbonates isomorphous thereto.

4 In testimony whereof, I have hereunto sub- 1 scribed my name this 10th da of July 1928. MARK N. FREDIENBURGH.

cent aqueous solution containingbar'ium and strontium nitrates in approximately equal amounts and from .-5 to 20.0 'per cent calciun'i' nitrate, heating said solution to temperatures approximating 85 0., adding thereto a sQlution of normal ammonium carbonate in excess to efiect the separation of ,the alkaline earth metal carbonate compounds and recovering the precipitated carbonate compounds therefrom in any s'uitable manner.

"15., The method offorming coarsely crystalline intimate admixtures of alkaline earth metal carbonate compounds which comprises precipitating an aqueous solution 'o'f barium, I 

